The present invention relates to a portable radio information terminal that has a radio communication function (radio section) and an information processing function (information processing section), and particularly to an antenna configuration for portable radio information terminals.
Conventionally, the portable radio information terminal of that type has the disadvantage in that noises radiated via an antenna from the information processing section adversely affect the radio section, particularly the receiving system, thus deteriorating the radio characteristics, particularly, the S/N ratio of a received radio signal (that is, deteriorating the receiving sensitivity).
One approach of solving that problem is to divide the portable radio information terminal into two parts including the main body and the cover. For example, the main body includes the information processing section and a display on the front surface of the main body. The cover is placed on the front surface of the main body and includes the radio section and an antenna. As generally used in the cellular telephones, the antenna selective diversity receiving system may be employed where plural antennas are disposed on the radio section and reception radio signals are received by selecting an antenna with a strong reception field strength.
FIG. 7 is a block diagram illustrating the configuration of a portable radio information terminal employing the above-mentioned technique.
In the portable radio information terminal, the information processing section is built in the main body while the radio section is built in the cover 2B. The cover 2B is mechanically coupled to the main body 1A by means of the shaft 20 such as a hinge shaft. The cover 2B is opened and closed to the front surface of the main body 1A by turning around the shaft 20 acting a rotating shaft.
The main body 1A includes a battery 3 acting as a power source for the information terminal and a control section 4B that processes information such as data or digital signals to be output from and input to the cover 2B. In the information terminal, the display 5 disposed on the display section of the main body 1A displays image information. A pressure sensitive device (e.g. touch panel) is attached on the display 5. The information processing procedure is performed by inputting the operation signal to the control section 4B via the input section 6. Normally, the information processing section consists of the control section 4B, the display section 5 and the input section 5, excluding the battery 3.
The cover 2B includes two antennas, that is, a whip antenna 7 being a whiplike conductor protruding from the cover 2B and an inverted-F antenna 9A disposed on the bottom (back) surface of the cover 2B. In the cover 2B, the radio section consists of a transmission section 13 that produces transmission radio signals, an antenna switch 16 that selects a reception radio signal received via the antenna 7 or 9, a receiving section 11 that converts a selected reception radio signal to a desired frequency and a desired level and then amplifies the converted signal acting as a received signal, a circulator 10 that transmits a transmission radio signal to the switch 16 and transmits a reception radio signal from the switch 16 to the receiving section 11, and a modulator and demodulator section 12 that modulates data or digital signal from the control section 4B and then transmits the modulated signal to the transmission section 13 and that demodulates a reception signal from the receiving section 11 and then transmits a digital signal being the demodulated data to the control section 4B. The demodulation section 12B includes a radio control section that controls the radio section. The radio control section selectively controls the frequency of a transmission signal and the frequency of a reception signal, controls the level of a radio signal output from the transmission section 13, and selectively controls the antenna switch 16. The circulator 10 acts as an isolator that prevents the input and output signals to and from the antenna 7 or 9 from being adversely affected by the receiving section 11 or transmission section 13 not involved in a transmission or receiving operation.
In the cover 2B, at the time of receiving radio signals, the receiving section 11 amplifies radio signals input from the antenna 7 or 9 via the circulator 10. Then the modulator and demodulator section 12B demodulates the amplified signal into a digital signal. The digital signal is output to the control section 4B of the main body 1A. At the time of transmitting radio signals, the modulation and demodulation section 12B modulates a digital signal output from the control section 4B of the main body 1A. The transmission section 13 amplifies the modulated signal as a transmission radio signal. Then the antenna 7 radiates the radio signal via the circulator 10.
The portable radio information terminal, shown in FIG. 7, performs the antenna selective diversity reception using two antennas 7 and 9A. The antenna switch 16 selects the antenna 7 or 9A to be connected to the receiving section 11 at the time of starting the receiving operation. The modulator and demodulator section 12B compares the level of a received signal from the receiving section 11. A desired signal is received by connecting the antenna with a stronger received signal level to the receiving section 11. Normally, since the receiving operation is changed for the transmission operation in a short period in milliseconds, an antenna with a larger received signal level is selected every changing mode.
Where the package is formed of a main body containing the information processing section and a cover for covering the main body and containing the radio section, the above-mentioned portable radio information terminal has the following disadvantage. That is, although the whip antenna can relatively and easily provide the good antenna gain, the metal portion in the main body disposed close to the whip antenna by closing the cover causes a decrease in the antenna gain. Moreover, when the antenna attached to the cover approaches the information processing section acting as a principal noise source of the main body, noises from the information processing section diffracts to the antenna, so that the receiving section of the radio section cannot stably receive reception radio signals.
In the antenna selective diversity reception using plural antennas, when the coupling between a high-gain antenna and the radio section is relatively strong, the use of the high-gain antenna induces the transmission radio signal diffracted from the high-gain transmission antenna to the receiving section. For that reason, in some cases, the constraint occurs that only the low-gain antenna must be used as a transmission antenna. Therefore even when the high-gain antenna decreases its gain due to the approach to the metal portion, the low-gain antenna is forced to be used for transmission.
In other cases, the antenna selective diversity receiving system where an inverted-F antenna is disposed in addition to the whip antenna may be employed for the portable radio information terminal. However, when the cover is in a closed state, noises (transmission radio signals) propagate from the whip antenna to the receiving section, so that the receiving section erroneously detects strong field strength due to the noises. As a result, the diversity reception cannot be stably performed. In order to judge whether or not the strong field strength results from noises or a desired signal, it may be considered to use the means of judging a received data ratio. However, this approach leads to the prolonged judgment time or complicated configuration.